The radio frequency (RF) spectrum is a limited commodity. Only a small portion of the spectrum can be assigned to each communications industry. The assigned spectrum, therefore, must be used efficiently in order to allow as many frequency users as possible to have access to the spectrum. Multiple access modulation techniques are some of the most efficient techniques for utilizing the RF spectrum. Examples of such modulation techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA).
Wireless service providers also seek other ways of using the available spectrum as efficiently as possible. One important technique for maximizing spectral efficiency is to minimize overhead message traffic. If the number of overhead messages transmitted is reduced, less overhead channels are required to carry overhead messages. This frees up spectrum for user traffic. Also, reducing the number of overhead messages reduces the processing load in both the mobile stations and the base stations of the wireless network. Spectral efficiency may also be improved by selecting the optimum modulation technique in order to maximize throughput and to minimize retransmissions of data.
The IS-95 wireless system (i.e., cdmaOne) was designed to support voice traffic. However, the next generation of wireless systems must support both voice and high-speed packet data services simultaneously. This poses an immense challenge in configuring a wireless system that is tuned and optimized for both services, since these services impose vastly different requirements.
Voice and simple data services (e.g., fax, asynchronous data) require only relatively low throughput (e.g., 8 Kbps to 13 Kbps). The throughput for these services is symmetric (i.e., similar data rates in the forward channel and reverse channel). Voice and simple data services also require low latency and uniform Quality of Service (QoS) for the entire duration of the service connection.
On the other hand, packet data services are generally asymmetrical, where the data rate on the forward channel (i.e., downlink) is much greater than the reverse channel (i.e., uplink). Also, the data throughput for packet data services is bursty in nature and can tolerate some degree of latency.
The 1x configuration of CDMA2000 supports data rates up to 614 Kbps for packet data services. However, CDMA2000-1x does not meet the 3G requirements for packet data services up to 2 Mbps. The 3x configurations of CDMA2000 support up to 2 Mbps and meet this 3G requirement. However, CDMA2000-3x configurations require three carrier frequencies (1.25 MHz) each, which increases the complexity of both the base station and the mobile station.
The high rate packet data (HRPD) system solves some of these issues, but it requires a different carrier frequency. Also, the HRPD cannot support real-time services and requires completely new technology and a new protocol stack. HRPD also introduces new network elements and newer interfaces into the network. Also, HRPD is not backwardly compatible with the IS-95 family of standards.
CDMA2000-EV/DV technology has been introduced to overcome these problems. CDMA2000-EV/DV supports simultaneous voice and data services and has higher data throughput than a HRPD system. The peak data rate in the current forward link framework proposal is up to 3.84 Mbps. To support higher data rates and throughput, the scheduling of users must be done efficiently. An efficient scheduling algorithm is needed to guarantee higher throughput and better handling of the number of data users and voice users.
There is therefore a need in the art for improved systems and methods for scheduling the transmission of data packets in the forward channel of a wireless network. In particular, there is a need for an efficient scheduling apparatus that achieves an optimum throughput by maximizing the forward channel transmission data rate without significantly increasing the number or re-transmissions.